Mince pies wait to be eaten before the Wookey Hole Big Eat Mince Pie Eating Contest on November 29, 2006 in Wookey Hole, near Wells, England. (Matt Cardy/Getty Images) It's time for the flakiest, crustiest food holiday of the year: Pi Day. In 1988, physicist Larry Shaw since to honor the endless mathematical constant. Since then, mathematicians have celebrated π, which rounds to 3.14, on March 14, a date that also happens to be Albert Einstein's birthday.